Honeycomb roll

ABSTRACT

A honeycomb roll is provided in which the honeycomb structure incorporates partitioning aligned with the roll axis and which may be formed to present the thinnest practical outer edges at the roll body surface in combination with inner edges of substantially greater thickness for enhancing the effect of suction influence applied through the honeycomb structure. The preferred embodiment employs a plurality of specially formed annular members secured in assembled relation as a honeycomb structure in roll body form.

[ Aug. 13, 1974 HONEYCOMB ROLL [75] Inventor: Dieter F. Zeiffer, Charlotte, N.C.

[73] Assignee: Gaston County Dyeing Machine Company, Mt. Holly, N.C.

[22] Filed: Feb. 22, 1973 [21] Appl. No.: 334,955

52 US. Cl 29/121 R [51] Int. Cl B211) 27/02 [58] Field of Search 29/121 R, 121 A, 125

[56] References Cited UNITED STATES PATENTS 2,581,754 l/1952 Cosmos 29/121 R 3,016,315 l/l962 Robinson 29/121 R X 3,100,928 8/1963 Bryand 29/121 R X 3,105,043 9/1963 Rich et al. 29/121 R X 3,139,375 6/1964 Bryand 29/121 R X Bryand 29/121 R Beck 29/121 R Primary Examiner-Alfred R. Guest Attorney, Agent, or Firm-Richards, Shefte & Pinckney [57] ABSTRACT A honeycomb roll is provided in which the honeycomb structure incorporates partitioning aligned with the roll axis and which may be formed to present the thinnest practical outer edges at the roll body surface in combination with inner edges of substantially greater thickness for enhancing the effect of suction influence applied through the honeycomb structure. The preferred embodiment employs a plurality of specially formed annular members secured in assembled relation as a honeycomb structure in roll body form.

14 Claims, 9 Drawing Figures PAINTED Alli; I 3 i974 SHEEI 2 OF 2 a, i s Hi,

1 HONEYCOMB ROLL None; although copending application Ser. No. 240,010, filed Mar. 31, 1972, now U.S. Pat. No. 3,755,869, issued Sept. 4, 1973, describes and claims an alternative honeycomb roll structure of generally related interest.

BACKGROUND OF THE INVENTION Honeycomb rolls find considerable use for extraction or drying purposes, as in dealing with textile web material after washing. As heretofore provided such rolls have commonly been formed by constructing a network of relatively thin straight and undulated strips that were alternated in honeycomb fashion and supported between end members or on some sort of spider structure. Sometimes only alternately reversed undulating strips have been used in forming the honeycomb network. Representative examples are illustrated and described in U.S. Pat. Nos. 3,259,961 and 3,100,928.

The honeycomb network has the significance of providing a roll surface of high percentage open area that results in handling web material thereat in a substantially even manner so that surface patterns which might otherwise form in the web during subsequent handling are prevented. However, the prior practice of forming the honeycomb networks from a system of strips as mentioned above is quite expensive because of the great amount of labor involved, and the present invention materially reduces costs in this respect while providing a roll structure which is sturdier and more easily adapted to varying sizes and circumstances, as well as being considerably simpler than that disclosed in the above-noted copending application and also readily adaptable for applying suctionat the roll surface to the best advantage.

SUMMARY OF THE INVENTION In preferred form, the honeycomb roll of the present invention incorporates a plurality of annular members each having a base portion in the form of a planar oriented annulus from the full width of which rectangular and radially oriented partition portions extend perpendicularly in regularly spaced relation, which are assembled and fixed in series on a common axis with the partition portions aligned to provide a honeycomb structure in roll body form.

The honeycomb structure thus provided includes partitioning aligned with the axis of the roll body that may be formed to present the thinnest practical outer edges at the roll body surface in combination with inner edges of substantially greater thickness so as to make the most effective and efficient use of suction applied through the honeycomb structure for extraction or drymg.

The relative thinness at the outer edges of the honeycomb structure is significant in several respects. In the first place, these outer edges must afford adequate support at the roll surface for the material being handled thereat under the conditions imposed by the use to which the roll is being put, so that the outer edges cannot be thinner than will allow them to afford such support. Also, the permissible outer edge thinness is, of course, affected by the physical capacity of the material used in constructing the honeycomb to provide outer edges of sufficient strength and serviceability, and a related design factor will be the outer edge spacing selected for the particular processing conditions contemplated.

On the other hand, however, it is desirable that the outer honeycomb edges be as thin as possible in order to maximize the open area percentage at the roll surface so that material being handled thereat sees as little supporting surface as possible and is consequently subjected as evenly as possible to the suction influence applied through the honeycomb structure for extraction or drying.

Accordingly, by the thinnest practical outer edges it is meant that the outer honeycomb edges are formed as thin as the physical capacity of the material from which they are formed will allow consistent with adequate support of the material to be handled at the honeycomb surface in light of the particular honeycomb design being used and the nature of the processing to be performed. Similarly, in referring to partitioning having inner edges of substantially greater thickness so as to make the most effective and efficient use of suction applied through the honeycomb structure it is meant that, beyond designing sufficient structural strength into the partitioning, the inner edges of the axially aligned partitioning are also made enough thicker than the outer edges so that the suction influence can be localized effectively at one or more of the spacings therebetween to use the available suction in relation to material being handled to the best advantage, as described further below.

The preferred embodiment of the present invention, which allows size and open area percentage and strength to be selected with great flexibility in relation to the conditions of contemplated use, is also described further below in connection with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration exemplifying the manner in which honeycomb rolls embodying the present invention may be used;

FIG. 2 is a side elevation, partially broken away, of a honeycomb roll constructed in accordance with the preferred embodiment of the present invention;

FIG. 2a is an enlarged sectional detail of a sufficient portion of FIG. 2 to show more clearly the assembly arrangement of the annular members;

FIG. 3 is a partial section detail of one of the annular members substantially as seen at the line 3-3 in FIG. 2; FIG. 4 is a fragmentary side view as seen from the left in FIG. 3, in relation to which a dotted line representation of a suction slot is added;

FIG. 5 is an enlarged and partly sectioned detail taken substantially at the line 5-5 in FIG. 4;

FIG. 6 is a plan view corresponding to FIG. 5; and

FIGS. 7 and 8 are respective rightand left-hand elevations corresponding to FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1 of the drawings, a honeycomb roll is represented at 10 arranged with a stationary suction box 12 therein for extraction purposes, with a following larger sized honeycomb roll arranged for drying, so that a textile web W may be trained over them successively as shown for extraction and drying following washing or the like. The illustrated arrangement is such that a high velocity air flow is pulled through the honeycomb network of the roll by the suction box 12 to extract a good percentage of the moisture ahead of the drying stage and thereby materially lessen the drying load.

The drying roll 100 is suitably arranged within a bank of heater lamps 102 or the like shielded by a hood 104 and extending about roll 100 for substantially the full extent of the warp of web W thereon. Internally the roll 100 is provided with a suction means at 106 and a stationary baffle at 108 that reaches arcuately within that portion of the roll circumference at which the web W does not wrap, so that the suction means 106 induces a low velocity air flow between the heater bank 102 and the remaining circumferential portion of the honeycomb network of roll 100 to dry the web W before it is taken away over an idler 110.

Honeycomb rolls embodying the present invention are readily constructed to serve effectively as either the extraction roll 10 or the drying roll 100 in arrangements of the foregoing sort, or in any other situation in which honeycomb rolls have heretofore found use. FIG. 2 indicates the general arrangement of a preferred embodiment constructed in accordance with the present invention in which a plurality of the previously mentioned annular members are shown in fragmentary section at 14 assembled to constitute the roll body 16 and form a honeycomb network at the working surface thereof as diagramed partially at 14'.

For assembling the annular members 14, a pair of end flanges 18 is provided on which annular shoulder portions 20 are formed to fit the inner diameter of the annular members 14 so as to extend within the end members of the assembly and center the same at the flanges 18. Also, the end flanges 18 are apertured, in alignment with assembly bores in the annular members 14 as will be noted further presently, to receive tie rods 22 that are threaded at both ends and-extended through the annular members 14 and through the end flanges IS with nuts 24 engaging the threaded tie rod ends in back of the flanges 18 and biasing means 26 interposed between one of the nuts 24 and the back of the adjacent end flange and compressed thereat to tension the tie rods 22. A plurality of disc springs is advantageously used as the biasing means 26 because of the relatively level spring rate provided in this way, and in consequence of which the tightening of nuts 24 to compress the interposed biasing means to a particular length can be depended on to impose a desired tension load on the tie rods 22 rather closely. Such tensioning of tie rods 22 acts to rigidify the assembled annular members 14 in roll form quite satisfactorily.

In addition, the end flanges 18 are formed for centering in turn on mounting flanges 28 and securing thereto by screws as at 30. One of the mounting flanges 28 also carries a sprocket member 32 at which the drive for rotating the roll is introduced, and both mounting flanges 28 are fitted interiorly with a bearing unit 34 at which the roll structure is supported for rotation by a suitable spider arrangement (not shown) radiating from an axial member 36 extending through the roll structure between attaching flanges 38 provided at each end for installation of the roll structure on the frame on the equipment in which it is to be used. The axial member 36 also serves as part of the suction system and is provided in tubular form for this purpose so that it may be tapped adjacent either or both ends for connection with a suitable vacuum source (not shown) to impose the applied suction at a connected suction box comparable to that indicated at 12 in FIG. 1, or simply adjacent the roll axis as indicated at 106 in FIG. 1.

The remaining drawing illustrations detail further the general form of the annular members 14 and particulars of their preferred form. FIGS. 3 and 4 show these members 14 generally to comprise a base portion 40 in the form of a planar oriented annulus, and rectangular and radially oriented partition portions 42 extending perpendicularly from the full annulus width in regularly spaced relation, with the previously mentioned assembly bores for tie rods 22 formed at 44 through the base and partition portions 40 and 42 adjacent the inner edges thereof.

FIGS. 5 to 8 provide enlarged illustrations of the particular form of annular member base and partition portions 40 and 42 that is preferred. Because the annular members 14 are preferably formed of molded plastic the partition portions 42 are tapered in the direction of their extent (see FIGS. 6 and 7) to provide the necessary molding draft, apart from any structural consideration. Additionally, however, both the base and partition portions 40 and 42 are tapered toward their outer edges 46 and 48 to present the thinnest practical edges at the working surface of roll body 16, as noted earlier, to minimize the area of contact with fabric or other material being handled at which the extracting or drying influence applied through the honeycomb structure is blocked or lessened. In general, it is desirable, and entirely feasible, to provide a thinness of these outer edges 46 and 48 in the order of H32 inch or less.

As to perpendicular extent, the partition portions 42 are proportioned, within the strength characteristics of the material from which they are formed, to provide the annular members 14 as suitable modules of roll body length. For example, annular members 14 designed according to the present invention for use in forming an extraction roll having a diameter of about 12 inches and a length of about inches were proportioned with a base portion annulus width of Va inch and a partition portion extent sufficient to provide an annular member width or thickness in the roll length dimension of about /2 inch so that any particular roll length desired could be obtained readily by simply using the number of annular members 14 needed to produce it.

Spacing of the radially oriented partition portions 42 in the foregoing exemplary design was set at 3.0", or pitches about the base portion annulus, so as to provide honeycomb openings at the roll surface that are approximately square. The object in any case is to maximize open roll surface area so that the material to be handled thereat is not subjected to any unduly different influence at the outer base and partition portion edges 46 and 48 under the conditions of roll use. As the above-noted exemplary design was intended for use in forming an extraction roll which would involve inducing a relatively high velocity suction influence at the roll surface, the partition portion extent and spacing needed to be designed for adequate working surface support of the material being handled against this influence. In larger roll structures, of say 36 inches diameter such as are used for drying that requires only a relatively low velocity suction influence, the honeycomb openings can be larger and the 30 partition portion spacing could probably be maintained at a 36 inches diameter with proportionate lengthening of the partition portion extent to provide an approximately square opening and a suitable length module. In any event, prior experience with the use of honeycomb rolls has established quite fully' the extent of working surface open area that is tolerable under varying conditions of roll use, and the present invention makes it possible to simplify honeycomb roll construction materially while following previously established experience as to permissible open area extent.

In order to increase structural strength against the torsion load resulting from the end drive at the sprocket member 32, the extending edges of the partition portions 42 are preferably formed with central ribs 50 raised lengthwise thereof, and the opposite side of the base portion 40 from which the partition portions extend with complementary grooves 52 aligned therein for interfitting with the ribs 50 when the annular members 14 are assembled in roll form. The ribs 50 terminate short of the outer partition portion edges 48, so as not to interfere with the narrowing taper adjacent these outer edges, they merge inwardly with extending edge portions 54 that are raised at full width to the height of ribs 50 adjacent the inner partition portion edges. in addition, the side of base portion 40 opposite that from which the partition portions 42 extend is annularly relieved at 56 adjacent the inner edge thereof in a complementary extent for receiving the raised extending edge portions 54 upon assembly of the annular mem-.

bers 14. Also, it should be noted that the aligned assembly bores 44 open through the base and partition portions 40 and 42 at the annular relief 56 in the former and the raised extending edge portion 54 in the latter. The result is an interfitted keying of the annular members 14 upon assembly that not only strengthens the assembly nicely against the torsion load imposed by the drive as previously mentioned, but that also effects and maintains an aligned centering of the annular members 14 as they are assembled, so that the tie rods 22 are substantially relieved of any function or resulting stress other than that of supplying an adequate assembly tension lengthwise of the roll body and only relatively small size tie rods 22 (e.g., about 1/16 inch diameter) are needed for this purpose.

While the foregoing tie rod assembly arrangement is an exceptionally simple and effective one, particularly for relatively long rolls, other assembly means can be employed whenever desired and may even be preferable for short roll lengths. For example, the annular members 14 can be secured in series by adhesive or, if formed of plastic, they can be fused or designed for snapping together in interlocking relation. When the annular members 14 are formed of plastic as preferred, the plastic used needs to be selected for adequate temperature and chemical resistance under the conditions to be encountered during contemplated use, but such selection is readily made among the numerous plastic materials commercially available. The tie rods 22 are suitably formed of stainless steel wire, and the remaining parts of the FIG. 2 assembly of such materials as have heretofore been commonly used for comparable parts of honeycomb roll structures.

It should also be noted that in addition to forming the annular member partition portions 42 in sufficient thickness towards their inner edges to allow extension of the assembly bores 44 therethrough, and to provide these portions in general with adequate structural strength, the thickness at the inner partition portion edges may be made substantially greater than that at the outer edges for enhancing suction influence, as mentioned earlier. Such inner edge proportioning is not of particular importance when the honeycomb roll is to be used for drying because volume of flow is more important than velocity for drying purposes, but when extraction is involved velocity assumes primary importance and the significance of substantially thicker inner partition edges in this connection can be visualized best in relation to FIG. 4.

In FIG. 4, the partition portions 42 are represented in stylized form with an inner edge thickness that is substantially equal to the circumferential spacing therebetween, and a dotted line representation is added at 12' of a suction slot equal in width to the spacing width and defined by parallel walls having a thickness equal to the inner edge thickness. The suction slot 12' should be visualized as extending from a manifold arranged axially of the roll in sufficient capacity to cause application of available suction uniformly through slot 12 lengthwise of the roll.

With suction slot 12' stationary and annular member 14 rotating as the roll is driven, the illustrated FIG. 4 condition will result in applying the full force of the available suction momentarily at the spacing between the involved partition portions 42. Continued roll movement, however, will cause the involved partition portions 42 to shift from the illustrated alignment so that the trailing partition portion 42 begins to throttle the suction slot 12' and finally progresses to the point of closing it. During this period, if a level amount of power is expended in developing the available suction, as is normally the case, the throttling and ultimate closing of the suction slot 12 will cause a negative pressure increase in the suction system. Then, as the previously trailing partition portion 42 becomes the leading one and begins to open the suction 12' at the next spacing, the available suction will be progressively applied through this next spacing to reach the full force condition again at alignment therewith, and such suction application is repeated from spacing to spacing.

The result is a pulsating application of the available suction to the material being handled at the roll surface, which is particularly advantageous for extraction purposes, and which employs the power devoted to maintaining suction to the best advantage. The best advantage is obtained in the latter connection because the dissipation or lessening of suction pressure that necessarily occurs as the suction slot 12' reaches full alignment at each partition portion spacing is, or can be, balanced by the increase in suction pressure that occurs during throttling and ultimate closing of suction slot 12 as such alignment is passed in the course of the partition portion movement that progressively brings the next spacing into alignment. Thus, the suction available for application at each spacing is continually renewed as the roll rotates for effective and efficient use of power input at a given level.

Additionally, the pulsating application of suction that results has the advantage of building the suction influence at each spacing to a high velocity peak that induces excellent extraction action. Basically, effective extraction or drying depends on drawing an adequate mass per unit of time through the honeycomb structure for the purpose at hand. In the case of drying, heat is 3. In a honeycomb roll, the improvement defined in claim 2 in which aligned assembly bores are formed through said partition portions and the base portions thereat, in which a pair of end flanges is provided, and in which tie rods are extended through said assembly bores and secured at said end flanges to fix said annular member series in assembled roll body form.

4. In a honeycomb roll, the improvement defined in claim 2 in which said base and partition portions are talocity, and it is obtained even more effectively if the high velocity suction application is applied suddenly or rapidly, and it is for this reason that the pulsating application noted above is particularly advantageous.

It is not necessary that the partition portion inner edges and suction slot 12 be related precisely as indicated in FIG. 4 in order to obtain the pulsating advantage. In the exemplary design mentioned earlier, the partition portions 42 were formed with inner edges about 3/32 inch thick, with a resulting spacing therebetween of about 3/ 16 inch, and the related suction slot 12 was formed about A inch wide between walls about 1/8 inch thick, to provide very satisfactory results. The necessary requirement is that the partition portion inner edges have a thickness substantial enough to provide for the pulsating suction application noted above.

It should also-be mentioned that the particular nature of the material to be handled can have an effect on the degree of suction that is required or desired, as the type of material as well as the character of the moisture with which it is wet can vary the extraction action that is needed. For this reason, it may be desirable in some cases to arrange the suction slot with a width sufficient to draw simultaneously at more than one spacing, and in others to provide more than one suction slot space to draw at different spacings, but in any event the honeycomb roll of the present invention is readily adaptable for such variations with all of the described advantages.

The present invention has been described in detail above for purposes of illustration only and is not intended to be limited by this description or otherwise to exclude any variation or equivalent arrangement that would be apparent from, or reasonably suggested by, the foregoing disclosure to the skill of the art.

I claim:

1. In a honeycomb roll, the improvement comprising a roll body having a honeycomb structure of tubular configuration incorporating regularly spaced and radially oriented partitioning aligned with the axis of the roll body, all said partitioning presenting the thinest practical outer edges to maximize open area at the roll body surface in combination with inner edges of substantially greater thickness to allow the most effective and efficient use of suction applied through the honeycomb structure.

2. In a honeycomb roll, the improvement comprising a roll body having a honeycomb structure of tubular configuration incorporating a plurality of annular members each having a base portion in the form of a planar oriented annulus from the full width of which rectangular and radially oriented partition portions extend perpendicularly in regularly spaced relation, and means for assembling and fixing said annular members in series on a common axis with the partition portions thereof aligned.

pered to present the thinest practical outer edges at the surface of said roll body.

5. In a honeycomb roll, the improvement defined in claim 4 in which the thinness of said base and partition porltion outer edges is in the order of about 1/32 inch or ess.

6. In a honeycomb roll, the improvement defined in claim 4 in which said partition portions are also formed to present inner edges of substantially greater thickness.

7. In a honeycomb roll, the improvement defined in claim 6 in which the thickness of said partition portion inner edges is in the order of about 3/32 inch or more.

8.In a honeycomb roll, the improvement defined in claim 2 in which the perpendicular extent of said partition portions is proportioned within the strength characteristics of said portions to form said annular members as suitable modules of roll body length.

9. In a honeycomb roll, the'improvement defined in claim 4 in which the outer edge thinness and the spacing of said partition portions is selected to maximize open roll surface area to the fullest extent possible under the contemplated conditions of roll use.

10. In a honeycomb roll, the improvement defined in claim 3 in which the extending edges of said partition portions have central ribs raised lengthwise thereof and the side of said base portion opposite said partition portions has complementary grooves aligned therein for interfitting with said ribs when said annular members are assembled in roll body form.

11. In a honeycomb roll, the improvement defined in claim 10 in which the ribs raised at the extending partition portion edges terminate short of the outer partition portion edges and merge inwardly with a portion of said extending edges that is raised at full width to the height of said ribs adjacent the inner partition portion edges, and in which the side of said base portion opposite said partition portions is annularl relieved ad acent the inner edge thereof in a comp ementary extent for receiving said inner raised extending edge portions when said annular members are assembled in roll body form.

12. In a honeycomb roll, the improvement defined in claim 11 in which said aligned assembly bores open through said base and partition portions at the annular relief in the former and the inner raised extending edge portion of the latter.

13. In a honeycomb roll, the improvement defined in claim 3 in which said end flanges are formed with an annular shoulder pro ortioned in relation to the inner diameter of said annu ar member so as to extend within the end members of said plurality and center the same at said flanges.

14. In a honeycomb roll, the improvement defined in claim 13 in which said end flanges are apertured in alignment with said aligned assembly bores, and in which said tie rods are threaded at both ends and extended through the assembly bores of said annular member plurality and through the apertures of said end flanges with nuts engaging the threaded tie rod ends in back of said flanges and biasing means interposed between one of said nuts and the back of one flange and compressed thereat to tension said tie rods. 

1. In a honeycomb roll, the improvement comprising a roll body having a honeycomb structure of tubular configuration incorporating regularly spaced and radially oriented partitioning aligned with the axis of the roll body, all said partitioning presenting the thinest practical outer edges to maximize open area at the roll body surface in combination with inner edges of substantially greater thickness to allow the most effective and efficient use of suction applied through the honeycomb structure.
 2. In a honeycomb roll, the improvement comprising a roll body having a honeycomb structure of tubular configuration incorporating a plurality of annular members each having a base portion in the form of a planar oriented annulus from the full width of which rectangular and radially oriented partition portions extend perpendicularly in regularly spaced relation, and means for assembling and fixing said annular members in series on a common axis with the partition portions thereof aligned.
 3. In a honeycomb roll, the improvement defined in claim 2 in which aligned assembly bores are formed through said partition portions and the base portions thereat, in which a pair of end flanges is provided, and in which tie rods are extended through said assembly bores and secured at said end flanges to fix said annular member series in assembled roll body form.
 4. In a honeycomb roll, the improvement defined in claim 2 in which said base and partition portions are tapered to present the thinest practical outer edges at the surface of said roll body.
 5. In a honeycomb roll, the improvement defined in claim 4 in which the thinness of said base and partition portion outer edges is in the order of about 1/32 inch or less.
 6. In a honeycomb roll, the improvement defined in claim 4 in which said partition portions are also formed to present inner edges of substantially greater thickness.
 7. In a honeycomb roll, the improvement defined in claim 6 in which the thickness of said partition portion inner edges is in the order of about 3/32 inch or more.
 8. In a honeycomb roll, the improvement defined in claim 2 in which the perpendicular extent of said partition portions is proportioned within the strength characteristics of said portions to form said annular members as suitable modules of roll body length.
 9. In a honeycomb roll, the improvement defined in claim 4 in which the outer edge thinness and the spacing of said partition portions is selected to maximize open roll surface area to the fullest extent possible under the contemplated conditions of roll use.
 10. In a honeycomb roll, the improvement defined in claim 3 in which the extending edges of said partition portions have central ribs raised lengthwise thereof and the side of said base portion opposite said partition portions has complementary grooves aligned therein for interfitting with said ribs when said annular members are assembled in roll body form.
 11. In a honeycomb roll, the improvement defined in claim 10 in which the ribs raised at the extending partition portion edges terminate short of the outer partition portion edges and merge inwardly with a portion of said extending edges that is raised at full width to the height of said ribs adjacent the inner partition portion edges, and in which the side of said base portion opposite said partition portions is annularly relieved adjacent the inner edge thereof in a complementary extent for receiving said inner raised extending edge portions when said annular members are assembled in roll body form.
 12. In a honeycomb roll, the improvement defined in claim 11 in which said aligned assembly bores open through said base and partition portions at the annular relief in the former and the inner raised exteNding edge portion of the latter.
 13. In a honeycomb roll, the improvement defined in claim 3 in which said end flanges are formed with an annular shoulder proportioned in relation to the inner diameter of said annular member so as to extend within the end members of said plurality and center the same at said flanges.
 14. In a honeycomb roll, the improvement defined in claim 13 in which said end flanges are apertured in alignment with said aligned assembly bores, and in which said tie rods are threaded at both ends and extended through the assembly bores of said annular member plurality and through the apertures of said end flanges with nuts engaging the threaded tie rod ends in back of said flanges and biasing means interposed between one of said nuts and the back of one flange and compressed thereat to tension said tie rods. 